Find where the image of a car is.

A car's convex side mirror has a radius of curvature of 2 m. Another car is 9 m behind it. Its image is formed:

Answer: 0.9 m behind the mirror, one tenth the size.

For a convex mirror the focal length is +R/2 = +1 m in the New Cartesian sign convention, and the object distance is u = −9 m.

\frac{1}{v} = \frac{1}{f} - \frac{1}{u} = \frac{1}{1} + \frac{1}{9} = \frac{10}{9}

\Rightarrow v = + 0.9 m

m = - \frac{v}{u} = \frac{0.9}{9} = 0.1

The image is virtual and upright, 0.9 m behind the mirror and one tenth the size of the car. A sign slip in the mirror formula gives the 1.125 m answer instead.

Original practice question · JEE Physics Decoded

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